UI.WPF.Modern

• Added property `TreeViewItemHelper.ExpandChevronPadding
• Added the following resource keys to ThemeKeys
  • SystemControlBackgroundChromeMediumLowBrush
  • SystemControlBackgroundAltHighBrush
  • BaseWindowStyle
  • AeroWindowStyle
  • DefaultTreeViewItemStyle
  • DefaultTreeViewStyle
  • AutoSuggestBoxTextBoxStyle
  • DefaultToolTipStyle
  • TabItemPivotStyle
  • ToolBarOverflowButtonStyle
  • ToolBarThumbStyle
• Fixed some bugs

• Fixed the issue of NavigationView displaying PaneToggleButton incorrectly
• Added support for .NET Framework 4.5.2

• Use IsFooterSeparatorVisible to control visibility of the separator in NavigationView. If it is set to null, the system will decide whether to show or not
• Fix some issues

Now Fluent 2 Components are ALL AVAILABLE!

Special Thanks to:
@Kinnara @wherewhere @NotYoojun